ENIG Solderability Issues

Hello All, looking for some help from you guru's. I have several Enig boards with solderability problems. Components ranging from 0402's to ssop's. Using AIM W/S leaded solder paste, profile is beautiful and has been for years running the same product, full wetting occuring, solder joint is perfect for class 3 leaded process. When pressure upwards or sideways is applied component breaks free leaving a nickel looking pad exposed with the remainder of some fillet left behind.Black pad is likely. We have experienced problems with a particular board house in the past, who ran tests on copper, nickel, gold stackup and thickness and found they were all to spec. One particular date code on 3 different products showed this same problem. Problem went away for months and has returned. This time boards were sent out and analysed and the presence of silicone was detected. My questions are, has anyone ever experienced this occurance and 2 where could silicone contaminants possibly come from in the process. more info avail. if requested. Thanks.